High Ketones are caused by high blood sugars
(and lack of insulin). They occur because your body starts to break down fat
(and muscle) in preference to using the sugar in your blood, which in cannot
access easily without insulin.

Ketones are usually associated with sickness, or in the case of users of
Insulin Pumps, with a blocked line or infected
site. They can also result from ineffective insulin (that has been left in
the heat or well past its expiry date).

High Ketones are treated by giving a larger-than-normal dose of insulin
until the ketones disappear. How much you need to increase by is highly
individual, but can vary from 25% to 100% extra insulin.